The present invention pertains to a multilayered composite sandwich structure with embedded electronics, which can be used as flat sandwich circuit cards, multifunctional structure with embedded electronics or avionics, and complex shaped component housings with embedded electronics. Some examples of uses include aircraft sandwich bulkhead structure with embedded avionics, automotive instrument display panels with embedded electronics, aircraft instrument consoles, and flat sandwich circuit cards.
Circuit boards are one type of known composite structure that include electronics and may have composite materials with low dielectric properties. Electrical grade composite laminates are produced using a large variety of reinforcements, resin systems and thickness depending on end usage. Laminates are produced by stacking sheets of prepreg (fiber performs pre-impregnated with resin) between pre-treated copper foils of the desired thickness. A common type of printed circuit board produced today is a multi-layered board made of fiberglass and epoxy resin called “G10-FR4”. Most circuit boards, which are exposed to temperature fluctuations, are limited in thickness and the number of embedded circuits due to mismatch in coefficients of thermal expansion (CTE) between the vertical through hole via conductors and the laminate. This causes the number of circuit layers in a circuit card to be limited to prevent excessive thermal expansion and resulting via cracking. The CTE mismatch in conjunction with thermal distortion of the laminate causes cyclic strain on the solder joints of the electronic components. In harsh environments, thermal distortion of the board, CTE mismatch, and vibration result in solder joint fatigue failure.
Another type of known composite structure and one that may be utilized with the present invention is a polymer structural composite that may include carbon or glass fiber reinforced polymers that can be fabricated at relatively low temperatures. In most Aerospace applications, these structures are fabricated by laying up multiple layers of carbon fabric or unidirectional materials to form laminate structure. In other applications, such as most automotive or transportation uses, the composite structures are made by placing chopped and often randomly oriented fibers onto a mold. These fabric or random fiber performs are then resin infused, if not already impregnated with resin prior to lay-up onto the mold tooling, and then cured to create a rigid structure.
It is also known to bond composite laminates to each side of a core material to make composite sandwich structures. An example of one type of sandwich structure is corrugated cardboard. Composite structures as discussed above, may also be made into such a sandwich structure to create a lightweight yet stiff structure. The most common core materials include honeycomb cores, foams, and cellulous materials. Additionally, it should be appreciated that fabricating a composite structure includes the process of incrementally building up the material constituents onto mold tooling and may provide an opportunity to embed electronic components and their circuitry.
Presently, in aircraft, the electronics, which are commonly referred to as avionics, are not provided in the structural composite structures, but rather, housed in avionics boxes. These boxes are placed in avionics racks. The cost and weight of these boxes and racks can be substantial. The circuit cards provide the single function of securing the electronic components and circuitry and do not contribute to the strength or stiffness of the aircraft structure. In automobile instrument panels and aircraft instrument consoles electronic circuit cards are attached to the back of the panels or consoles and do not carry any load and do not contribute to the strength or stiffness of the assembly. It is, therefore, an object of the invention to provide a composite structure with embedded electronics. It is also an object of the invention that the electronics may be in embedded in structural composite structures such as found in aircraft. A further object of the invention is to reduce or eliminate the need and cost of avionics boxes by incorporating the avionics into composite structures.